Tag: physics

Questions Related to physics

The lightening conductor is connected to interface with ground or "earth" through

physics some natural phenomena lightning conductors lightning safety advanced of lightning

  1. a cathode

  2. an anode

  3. an electrode

  4. a semiconductor

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Correct Option: C
Explanation:

Conductor cables carry lightening current from lightening rod to the ground. Since electrode is an electrical conductor. So, the answer is "an electrode".

                      is engineered to protect an elevated structure in the event of lightning strike.

physics some natural phenomena lightning conductors lightning safety advanced of lightning

  1. A lightning conductor

  2. Copper wire

  3. A lightening shield

  4. All of the above

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Correct Option: A
Explanation:

A lightening conductor is a metal rod mounted on a structure and designed to protect the structure from lightening strike. 

If the instantaneous current in a metallic wire is $i = \left( {5 + 10t} \right)A$ then find amount of charge flown through it from $t = 2s$ to $t = 3s$ is

physics some natural phenomena lightning conductors lightning safety advanced of lightning

  1. 10 C

  2. 20 C

  3. 30 C

  4. 40 C

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Correct Option: C
Explanation:

Given instantaneous current,

$i=(5+10t)A$
and from the definition of instantaneous current,  $i=\dfrac { dq }{ dt } $
$\Rightarrow \quad \left( 5+10t \right) =\dfrac { dq }{ dt } $
$dq=\left( 5+10t \right) dt$
Integrating implies,
$Q=5t+{ 5t }^{ 2 }$
At $t=2$,
                ${ Q } _{ 1 }=30C$
At $t=3$,
                ${ Q } _{ 2 }=60C$

$\therefore $  Option (C) is the correct option.

Where is the lower end of a lightning conductor fixed in the building?

physics some natural phenomena lightning conductors lightning safety advanced of lightning

  1. at the top

  2. at a window

  3. at the base

  4. in the ground

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Correct Option: A
Explanation:

a) It made from metal like Iron.
b) Its top end is pointed.
c) Obviously on the top of building far from any other metal.
d) It is placed below the ground with a copper plate.

For cooking the food, which of the following type of utensil is most suitable 

conduction in metals and non-metals thermal energy transfers physics

  1. High specific heat and low conductivity

  2. High specific heat and high conductivity

  3. Low specific heat and low conductivity

  4. Low specific heat and high conductivity

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Correct Option: C

Two walls of thickness $d _1$ and $d _2$, thermal conductivities $K _1$ and $K _2$ are in contact. In the steady state if the temperature at the outer surfaces are $T _1$ and $T _2$, the temperature are the common wall will be 

conduction in metals and non-metals thermal energy transfers physics

  1. $\dfrac{K _1T _1+K _2T _2}{d _1d _2}$

  2. $\dfrac{K _1T _1d _2+K _2T _2d _1}{K _1d _2+K _2d _1}$

  3. $\dfrac{K _1d _1T _1+K _2d _2T _2}{K _1d _1+K _2d _2}$

  4. $\dfrac{(K _1d _1+K _2d _2)T _1T _2}{T _1+T _2}$

Show answer
Correct Option: B
Explanation:

$\begin{array}{l} { k _{ 1 } }\dfrac { { { T _{ 1 } }-{ T _{ c } } } }{ { { d _{ 1 } } } } ={ k _{ 2 } }\dfrac { { { T _{ c } }-{ T _{ 2 } } } }{ { { d _{ 2 } } } }  \ where\, { T _{ c } }\, is\, \, common\, \, wall\, temperature,\, solving\, for\, \, { T _{ c } }\, we\, \, will\, get \ { T _{ C } }=\dfrac { { { T _{ 1 } }+\alpha { T _{ 2 } } } }{ { \alpha +1 } }  \ u\sin  g\, \, \alpha =\dfrac { { { d _{ 1 } } } }{ { { d _{ 2 } } } } \dfrac { { { k _{ 2 } } } }{ { { k _{ 1 } } } }  \ { T _{ c } }=\dfrac { { { T _{ 1 } }+\dfrac { { { d _{ 1 } } } }{ { { d _{ 2 } } } } \dfrac { { { k _{ 2 } } } }{ { { k _{ 1 } } } } { T _{ 2 } } } }{ { \dfrac { { { d _{ 1 } } } }{ { { d _{ 2 } } } } \dfrac { { { k _{ 2 } } } }{ { { k _{ 1 } } } } +1 } }  \ =\dfrac { { { T _{ 1 } }\left( { { d _{ 2 } }{ k _{ 1 } } } \right) +{ T _{ 2 } }{ d _{ 1 } }{ k _{ 2 } } } }{ { { d _{ 1 } }{ k _{ 2 } }+{ d _{ 2 } }{ k _{ 1 } } } }  \ Hence,\, the\, option\, B\, is\, the\, \, correct\, answer. \end{array}$

The area of cross - section of rod is given by $ A = a _0 (1 + \alpha x )  $ where $  A _{ 0 }\quad & \quad \alpha  $ are constant and x is the distance from one end If thermal conductivity of material is K. What is the thermal resistance of the rod if its length is 

conduction in metals and non-metals thermal energy transfers physics

  1. $ KA _{ 0 }\alpha \quad to\quad (1+a\ell _{ 0 }) $

  2. $ \frac { 1 }{ Ka _{ 0 }\alpha } \quad \ell n \quad (1+\alpha\ell _{ 0 })$

  3. $ \frac { \alpha }{ KA _{ 0 } } \quad \ell n\quad (1+a\ell _{ 0 }) $

  4. $ \frac { KA _{ 0 } }{ \alpha } \ell n(1+\alpha \ell _{ 0 })$

Show answer
Correct Option: B
Explanation:

$\begin{array}{l} A={ a _{ 0 } }\left( { 1+\alpha x } \right)  \ dR=\dfrac { { dx } }{ { KA } }  \ =\dfrac { { dx } }{ { K{ \alpha _{ 0 } }\left( { 1+\alpha x } \right)  } }  \ =R=\dfrac { 1 }{ { K{ a _{ 0 } } } } \int _{ 0 }^{ { l _{ 0 } } }{ \dfrac { { dx } }{ { 1+\alpha x } }  }  \ =\dfrac { 1 }{ { \alpha K{ a _{ 0 } } } } \ln { \left( { 1+\alpha { l _{ 0 } } } \right)  }  \ =\dfrac { 1 }{ { K{ a _{ 0 } }\alpha  } } \ln { \left( { 1+\alpha { l _{ 0 } } } \right)  }  \ Hence, \ option\, \, B\, \, is\, correct\, \, answer. \end{array}$

a container that suits the occurrence of an isothermal process should be made of 

conduction in metals and non-metals thermal energy transfers physics

  1. Copper

  2. Glass

  3. Wood

  4. Cloth

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Correct Option: A

The temperature of skin is $T _{skin} = 34^0C$ (somewhat less than the body temperature, $T _{body} = 37^0C$) and the ambient tempreature is $T _{room} = 24^0C$. The surface area of an adult is A $\simeq$ 1.85 $m^2$. Calculate the net heat loss of the person.

conduction in metals and non-metals thermal energy transfers physics

  1. 25 W

  2. 100 W

  3. 300 W

  4. 500 W

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Correct Option: A

Consider a compound slab consisting of two different materials having equal thickness and thermals conductivities K and $2K$ in series. The equilvalent conductivity of  the slab is

conduction in metals and non-metals thermal energy transfers physics

  1. $\frac{2}{3}K$

  2. $\sqrt {2K} $

  3. $3K$

  4. $\left( {\frac{4}{3}} \right)K$

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Correct Option: C